Pulley unit having one-way clutch

ABSTRACT

A pulley unit comprises a pulley, a shaft relatively rotatable with the pulley and concentrically arranged inner side of the pulley, a one-way clutch interposed in an annular space between the pulley and the shaft, and a ball bearing arranged adjacent to the one-way clutch in an axial direction in the annular space. The ball bearing has an inner ring and an outer ring. Raceway curvatures of the inner and outer rings of the ball bearing are set to not less than 50.5% and not more than 52.0%.

FIELD OF THE INVENTION

The present invention relates to a pulley unit having a one-way clutch.The pulley unit can be mounted in an auxiliary machine which is drivenby a crankshaft of an engine of an automobile or the like through abelt. Examples of auxiliary machine are an air-conditioner compressor, awater pump, an alternator, a cooling fan and the like of an automobile.

BACKGROUND OF THE INVENTION

Various auxiliary machines mounted in automobile engines are driven byan engine crankshaft through a belt. Amongst the auxiliary machines, analternator is driven by an engine crankshaft so as to generateelectricity. When the alternator is coupled with the engine crankshaftso as to simultaneously rotate, as the number of rotation of thecrankshaft decreases, the power generating efficiency decreases. Inorder to prevent the decrease of the power generating efficiency, analternator having a one-way clutch in a pulley portion thereof has beendevised. As to the alternator, when the rotational speed of thecrankshaft lowers, the rotation of a rotor of the alternator iscontinued by inertial force so as to improve the power generatingefficiency thereof.

FIG. 10 shows a pulley unit. The pulley unit is equipped with a pulley1, a rotor shaft 2, a one-way clutch 3 and a deep groove ball bearing 44and a needle roller bearing 45. A cam face 10 is formed intermediate theaxial direction of an outer peripheral surface of a rotor shaft 2. Abelt 6 is wound around an outer periphery of the pulley 1. When the belt6 is driven by an engine crankshaft of an automobile not shown in afigure, the pulley 1 is rotationally driven. The rotor shaft 2 is fixedto a rotor of an alternator. The one-way clutch 3 has a cage 12 and aplurality of rollers 13 which are housed in a plurality of pockets ofthe cage 12 one each. The rollers 13 are always pushed to a narrow side(lock side) of a wedge-like space by a coil spring not shown in afigure. The wedge-like space is an annular space in a circumferentialdirection formed between an inner peripheral surface of an outer ring 11and the cam face 10 of the rotor shaft 2 so as to roll the rollers 13.The wedge-like space is narrowed to the lock side. The one-way clutch 3,the deep groove ball bearing 44 and the needle roller bearing 45 aresealed by a pair of seal rings 20, 21 and a seal annular body 22 andlubricated by a common lubricant.

In operation, when a rotational speed of the pulley 1 becomes relativelyfaster than the same of the rotor shaft 2, the rollers 13 of the one-wayclutch 3 are rolled to the narrow side of the wedge-like space and so asto be in a locked state. The locked state is a state in which the outerring 11 and the rotor shaft 2 can be integrally rotated via the rollers13. The outer ring 11 and the pulley 1 are integrally arranged. As aresult, the pulley 1 and the rotor shaft 2 are integrally rotated in thelocked state so that a rotational power can be transmitted from thepulley 1 to the rotor shaft 2.

When the rotational speed of the pulley 1 becomes relatively slower thanthe same of the rotor 2, the rollers 13 of the one-way clutch 3 arerolled to a broad side (free side) which is the apposite side from thenarrow side of the wedge-like space. As a result, the pulley unitbecomes in a free state. The free state is a state in which the outerring 11 and the rotor shaft 2 can freely rotate to each other. Thus,transmission of a rotational power from the pulley 1 to the rotor shaft2 is intercepted. In the case where the rotor shaft 2 is being rotatedprior to the interception, the rotor shaft 2 continues its rotation onlyby its own rotational inertial force after the interception.

Referring to FIGS. 10 and 11, the deep groove ball bearing 44 will bedescribed. The bearing 44 takes an axial load. The bearing 44 isequipped with an inner ring 50, an outer ring 51, a cage 56 and aplurality of balls 52. The inner ring 50 and the outer ring 51respectively have raceway grooves 53 and 54. The raceway grooves 53 and54 correspond to an arc of a circle 55 indicated by an imaginary linelarger than a diameter of the balls 52. In a case that a curvatureradius of the raceway grooves 53 and 54 is R and a diameter of the balls52 is D, a raceway curvature (%) of the raceway grooves 53 and 54 isexpressed as the formula (1).

Raceway curvature=(R/D)×100  (1)

According to the formula (1), when the raceway curvature is 50%, theradius of the balls 52 (D/2) and the curvature radius (R) of the racewaygrooves 53 and 54 are identical. Therefore, when the raceway curvatureis 50%, the balls 52 are fitted to the raceway grooves 53 and 54 with nogap. In this manner, when the raceway curvature is 50%, an axialdeviation of the bearing 11 becomes completely nil. In this state, theballs 52 are fitted to the raceway grooves 53 and 54 with no gap.Therefore, there are possibilities of a generation of a seizure on theraceway grooves 53 and 54 and of an undesirable influence on a servicelife of a lubricant due to a contact friction between the balls 52 andthe raceway grooves 53 and 54. In order to deal with this, theabove-mentioned raceway curvature is set to a range of 52.0-52.5% forthe raceway groove 53 of the inner ring 50, and to a range of 53.0-53.5%for the raceway groove 54 of the outer ring 51.

As shown in FIG. 12, the bearing 44 needs to be mounted by force-fittingbetween the pulley 1 and the rotor shaft 2. For the reason thereof, aradial internal clearance of the bearing 44 is set to a few times aslarge as a standard radial internal clearance with regard to atolerance. For example, in case of the bearing 44 having bearingdesignation 6807 in JIS (Japan Industrial Standard), a radial internalclearance before mounting thereof is set to 50-100 μm. When the bearing44 is force-fitted between the pulley 1 and the rotor shaft 2, theradial internal clearance decreases. Therefore, the radial internalclearance after mounting of the ball bearing 44 is set to a range ofapproximately 21-52 μm.

In the case where the deep groove ball bearing 44, in which the racewaycurvature of the raceway groove 53 is a range of 52.0-52.5%, the racewaycurvature of the raceway groove 54 is a range of 53.0-53.5%, and theradial internal clearance before mounting thereof is a range of 75-99μm, is mounted by force-fitting between the pulley 1 and the rotor shaft2, the radial internal clearance after mounting thereof is a range of21-52 μm and the axial internal clearance thereof is a range of 140-239μm, as shown in Table 7.

TABLE 7 radial internal clearance after axial internal mounting [μm]clearance [μm] 21˜52 140˜239

The axial internal clearance, as shown in FIG. 13, denotes the axialdeviation of the inner and outer rings 50 and 51 based upon racewaycurvatures and the radial internal clearance after mounting of racewaygrooves 53 and 54.

SUMMARY OF THE INVENTION

A main object of this invention is to provide a pulley unit capable ofdecreasing an axial deviation between a pulley and a shaft.

Other objects, features and advantages of the present invention will beapparent from the following description.

In summary, a pulley unit according to the invention comprises a pulley;a shaft which can be relatively rotated with the pulley and which isconcentrically arranged inner side of the pulley; a one-way clutch whichis interposed in an annular space between the pulley and the shaft; anda ball bearing which is disposed adjacent to the one-way clutch in anaxial direction in the annular space.

As for the pulley unit of the invention, firstly, raceway curvatures ofboth inner and outer rings of the ball bearing are set to not less than50.5% and not more than 52.0%. Secondly, a radial internal clearanceafter mounting of the ball bearing is set to less than 20 μm. Thirdly,both the first and second setting procedures are conducted to the ballbearing. Fourthly, the raceway curvatures of both the inner and outerrings of the ball bearing are set to not less than 50.5% and not morethan 51.0%. Fifthly, at least one of the raceway curvatures of the innerand the outer ring of the ball bearing is set to not less than 50.5% andnot more than 51.0%. Then, providing a curvature radius of the racewaygroove of the outer ring is Ro and a diameter of the ball is D, theraceway curvature of the outer ring is expressed as the formula(Ro/D)×100%. Similarly, the raceway curvature of the inner ring isexpressed as the formula (Ri/D)×100% with Ri for a curvature radius ofthe raceway groove thereof and D for a diameter of the ball.

In any of the setting, the axial internal clearance of the ball bearingbecomes small, wherein the axial deviation between the pulley and theshaft is reduced. As a consequence, this contributes to restricting aninclination of the pulley unit caused by a belt load and ultimately cansuppress a damage, a heat generation on the one-way clutch and thebearing, a shorter life of a lubricant, and a noise generation due to abelt vibration.

Preferably, the ball bearing is arranged in one side of the one-wayclutch, and the roller bearing is arranged in another side of theone-way clutch. The radial internal clearance after mounting of the ballbearing is set to a smaller value than the same of the roller bearing.The setting can reduce a rattle in the radial and the axial directionsof the ball bearing, whereby, the pulley and the shaft can be integrallystructured in order to improve a rigidity against a moment load.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects as well as advantages of the invention willbecome clear by the following description of preferred embodiments ofthe invention with reference to the accompanying drawings, wherein:

FIG. 1 is a sectional view of a pulley unit according to a preferredembodiment of the present invention.

FIG. 2 is a sectional view of the pulley unit along a line (2)—(2) ofFIG. 1.

FIG. 3 is a oblique view of a rotor shaft and a cage of a one-way clutchshown in FIG. 1.

FIG. 4 is a oblique view of a cage of a deep groove ball bearing shownin FIG. 1.

FIG. 5 is an explanatory drawing showing locked and free states ofrollers of a one-way clutch

FIG. 6 is a sectional view of a pulley unit according to anotherpreferred t of the invention.

FIG. 7 is a oblique view showing a rotor shaft and a cage of a one-wayclutch shown in FIG. 6.

FIG. 8 is a graph showing a relation between a radial internal clearanceafter mounting of a ball bearing and a life thereof.

FIG. 9 is a sectional view of a pulley unit according to a still anotherpreferred embodiment of the present invention.

FIG. 10 is a sectional view of a related art pulley unit.

FIG. 11 is a sectional view of a deep groove ball bearing.

FIG. 12 is an explanatory drawing of a radial internal clearance aftermounting.

FIG. 13 is an explanatory drawing of an axial internal clearance.

In all these figures, like components are indicated by the samenumerals.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A pulley unit according to a preferred embodiment of the invention withreference to FIGS. 1 to 5 will be described. A pulley unit includes apulley 1, a rotor shaft 2, a one-way clutch 3, a deep groove ballbearing 4 and a needle roller bearing 5.

The rotor shaft 2 is cantilevered as an example of a shaft. The rotorshaft 2 is relatively rotatable with the pulley 1 and concentricallyarranged inner side thereof. The pulley 1 serves as an outer annularbody, while the rotor shaft 2 serves as an inner annular body. An outerperipheral surface of the rotor shaft 2 includes three regions X1, X2,and X3. The region X1 is an intermediate region in the axial directionon which the one-way clutch 3 is mounted. The region X2 is one region inthe axial direction on which the ball bearing 4 is mounted. The regionX3 is the other region in the axial direction on which the rollerbearing 5 is mounted.

The one-way clutch 3 is interposed in the intermediate region X1 of anannular space between the pulley 1 and the rotor shaft 2. The one-wayclutch 3 is equipped with a cage 12, a plurality of rollers 13 and acoil spring 14. An inner peripheral surface of the pulley 1 and theouter peripheral surface of the rotor shaft 2 serves as raceways onwhich the rollers 13 of the one-way clutch 3 roll. Thus the pulley 1 andthe rotor shaft 2 are used as the inner and outer rings of the one-wayclutch. The cage 12 has pockets 12 a provided at several positions inthe circumferential direction thereof. The pockets 12 a penetrate insideand outside in the radial direction of the cage 12. The rollers 13 ofthe one-way clutch 3 are housed and held in the pockets 12 a one each.In the cage 12, a pillar member 12 b exists between the adjacent pockets12 a of the cage 12. A projection 12 c is integrally formed in an innerwall face of the pillar member 12 b. A coil spring 14 is mounted on theprojection 12 c of the cage 12. The coil spring 14 energizes the rollers13 to a narrow side (lock side) of a wedge-like space formed between acam face 10 of the rotor shaft 2 and the inner peripheral surface of thepulley 1.

The deep groove ball bearing 4, as one rolling bearing, is disposed inone side in the axial direction of and adjacent to the one-way clutch 3(which corresponds to the region X2) in the annular space. The deepgroove ball bearing 4 has a plurality of balls 23 and a cage 24. In theinner peripheral surface of the pulley 1 and the outer peripheralsurface of the rotor shaft 2, deep raceway grooves 25 and 26 are formed,wherein the rollers 23 of the deep groove ball bearing 4 roll. Accordingto the raceway grooves 25 and 26, the pulley 1 and the rotor shaft 2 arealso used as the inner and outer rings of the deep groove ball bearing4. The cage 24, as shown in FIG. 4, is formed into a crown shape, andhas a plurality of pockets 24 a for housing and holding the balls 23.

The needle roller bearing 5, as the other rolling bearing, is disposedin the other side in the axial direction of and adjacent to the one-wayclutch 3 (which corresponds to the region x3) in a free end side of thepulley unit A. The deep groove ball bearing 4 is arranged in anauxiliary machine side, for example, an alternator side. The needleroller bearing 5 has a plurality of rollers 33 and a cage 34. The innerperipheral surface of the pulley 1 and the outer peripheral surface ofthe rotor shaft 2 form raceways on which the rollers 33 of the needleroller bearing 5 roll. Thus the pulley 1 and the rotor shaft 2 are alsoused as the inner and outer rings of the needle roller bearing 5.

As described, the ball bearing 4 is arranged in a basic end side of therotor shaft 2, and the roller bearing 5 is located in a free end side ofthe rotor shaft 2.

The flat cam face 10 used for the one-way clutch 3 is formed at severalpositions in a circumference of the intermediate region X1 of the rotorshaft 2. Inner ring raceways of the ball bearing 4 and the rollerbearing 5 are secured in both side regions in the axial directions X2and X3 of the rotor shaft 2. The region X1 of the rotor shaft 2 has anoctagonal shape composed of eight cam faces 10. The regions, X2, X3 ofthe rotor shaft 2 constitute a cylindrical shape.

In order for the one-way clutch 3, the ball bearing 4 and the rollerbearing 5 to be easily incorporated in that order from one axialdirection between the pulley 1 and the rotor shaft 2, an outsidedimension of the region X2, of the rotor shaft 2 is set to be largerthan that of the region X3 thereof.

In the region X3 of the rotor shaft 3, a locating groove 40 is provided.An diametrically-inward ring-shaped projection 34 a is provided on aninner peripheral surface of the cage 34 of the roller bearing 5. Theprojection 34 a is engaged in the locating groove 40. Thus the cage 34is located in the axial direction. The inner peripheral surface of thecage 12 of the one-way clutch 3 is formed into an octagonal shape whichcoincides and fits to the outer shape of the region X1 of the rotorshaft 2. The cage 12 is fitted around the region X1 of the rotor shaft 2with a state in which the cage 12 holds the rollers 13. Thereby the cage12 is prevented from being rotated in the circumferential direction withrespect to the rotor shaft 2.

A tapered step 41 is formed between the cam surface 10 of the region X1and the region X2 of the rotor shaft 2. The cage 12 is prevented frommoving toward the ball bearing 5 by the step 41. Thus the cage 12 isprevented from moving toward the roller bearing 5 by the cage 34 of theroller bearing 5 located axially with respect to the rotor shaft 2.

The outer peripheral surface of the pulley 1 has a belt guiding face 39.The belt 6 shown in two dotted lines is wound around the belt guidingface 39. The pulley 1 is rotationally driven by an engine crankshaft ofan automobile. The rotor shaft 2 is fixed to the rotor of the alternatoras an example of an input shaft of auxiliary machines. The one-wayclutch 3 has a plurality of rollers 13 held in the cage 12. The cainface 10 is formed in the outer peripheral face of the rotor shaft 2 asmany in number as the rollers 13. Thereby a space in the radialdirection between the cam face 10 and the inner peripheral surface ofthe pulley 1 becomes narrower toward one side in the circumferentialdirection (a clock-wise direction in FIG. 2). The one side in thecircumferential direction is a lock side. The space in the radialdirection which becomes gradually narrower toward the lock side isstated a wedge-like space in this specification. The rollers 13 aredisposed in the wedge-like space between the cam face 10 and the innerperipheral surface of the pulley 1, and are energized to the lock sideby the coil spring 14. The one-way clutch 3, the deep groove ballbearing 4, and the needle roller bearing 5 are sealed by a pair of sealrings 20 and 21 and a seal annular body 22. The one-way clutch 3 andboth the bearings 4 and 5 are lubricated by a common lubricant.

In operation, when a rotational speed of the pulley 1 becomes relativelyfaster than that of the rotor shaft 2, the rollers 13 of the one-wayclutch 3 are rolled to the lock side of the wedge-like space as shown ina solid line in FIG. 5. When the rollers 13 are rolled to the lock sidein such a manner, the rollers 13 are caught between the inner face ofthe pulley 1 and the outer face of the rotor shaft 2 and cannot berolled. The state is referred to as a locked state. In the locked state,the pulley 1 and the rotor shaft 2 are rotationally integrated via therollers 13. In the locked state, the rotor shaft 2 cannot be freelyrotated and synchronously rotates with the pulley 1.

When the rotational speed of the pulley 1 becomes relatively slower thanthe same of the rotor shaft 2, the rollers 13 of the one-way clutch arerolled to a broad side of the wedge-like space, that is, an unlock side,as shown in an phantom line in FIG. 5.

The roll of the rollers 13 to the unlock side leads the rotor shaft 2 toa free state in which the rotor shaft 2 can be freely rotated withrespect to the pulley. In the free state, transmission of a rotationalpower from the pulley 1 to the rotor shaft 2 is intercepted. As aresult, the rotor shaft 2 continues its rotation by its own rotationalinertial force.

The raceway curvature of the deep groove ball bearing 4, and a relationbetween the radial internal clearance after mounting and the axialinternal clearance are explained in a few patterns. If the curvatureradius of the raceway grooves 25 and 26 is R, and the diameter of theballs 23 is D, the raceway curvature is explained in the followingformula as shown in the formula (1).

The raceway curvature=(R/D)×100

(1) In a case that the raceway curvatures of the raceway grooves 25 and26 are set to a small value

The raceway curvatures of the raceway grooves 25 and 26 are setrespectively to not less than 50.5% and not more than 52.0%. The radialinternal clearance after mounting is set to 0-30 μm. A relation betweenthe radial internal clearance after mounting (dim) and the axialinternal clearance (um) are shown in the following Table 1.

TABLE 1 radial internal clearance after axial internal mounting [μm]clearance [μm] 0  0 5 30˜62 10 42˜87 15 51˜106 20 58˜122 25 64˜136 3069˜149

According to Table 1, a range of an axial internal clearance in a rangeof a radial internal clearance after mounting 10 to 30 μm is 42-149 μm.The fact shows the range of the axial internal clearance becomesgenerally small, Fred to the range of the axial internal clearance,140-239 μm in the range of the radial internal clearance after mounting,21-52 μm shown in Table 7. When the radial internal clearance aftermounting is less than 10 μm, the axial internal clearance becomes evensmaller with 0-62 μm.

(2) In a case that a radial internal clearance after mounting is set toa small value

The radial internal clearance after mounting of a deep groove ballbearing 4 is set to less than 20 μm . In the same manner as conventionalexamples, the raceway curvature of the raceway groove 26 is set to52.0-52.5%, and the raceway curvature of the raceway groove 25 is set to53.0-53.5%. A value of the axial internal clearance in this case isshown in Table 2.

TABLE 2 radial internal clearance after axial internal mounting [μm]clearance [μm] 0  0 5  69˜76 10  97˜107 15 119˜130 20 137˜150

As apparent in Table 2, when a radial internal clearance after mountingis less than 20 μm, an axial internal clearance is 0-130 μm. When theradial internal clearance after mounting is less than 10 μm, the axialinternal clearance becomes smaller with 0-62 μm compared to conventionalexamples. Table 3 is shown as an example of comparison. In Table 3, aradial internal clearance after mounting is 21-52 μm, and an axialinternal clearance is 109-200 μm.

TABLE 3 radial internal clearance after axial internal mounting [μm]clearance [μm] 21˜ 52 109˜200

In case of a deep groove ball bearing 4 related to a radial internalclearance after mounting and an axial internal clearance shown in Table3, the ax internal clearance generates an axial deviation between thepulley 1 and the rotor shaft 2 by an axial vibration of the pulley unitdue to, for example, an engine vibration. As a result, the rollers 13 ofthe one-way clutch 3 and the rollers of the needle roller bearing 5 slipin the axial direction with respect to the inner and outer rings thereofso as to possibly deteriorate interlocking thereof with the inner andouter rings thereof and generate a vibration therefrom due to a windingroll.

The above-mentioned slip in the axial direction generates anexfoliation, an abrasion and a heat in the rollers 13 of the one-wayclutch 3, the rollers of the needle roller bearing 5 and the inner andouter rings thereof so as to possibly shorten a life of a lubricant.

(3) As a more preferable example, a value of the axial internalclearance is shown in Table 4 in a case that the raceway curvatures ofthe inner and the outer raceway grooves 25 and 26 of the deep grooveball bearing 4 are respectively, not less than 50.5%, and not more than51.0%.

TABLE 4 radial internal clearance after axial internal mounting [μm]clearance [μm] 0  0 5 30˜43 10 42˜61 15 51˜74 20 58˜85 25 64˜95 3069˜103

As apparent from Table 4, an axial internal clearance becomes smallercompared to the examples shown in Table 7, with a value thereof 42-103μm in a range of a radial internal clearance after mounting 10-30 μm. Asa more preferable example, it is identified that the axial internalclearance becomes smaller with a value thereof 0-85 μm in a range of theradial internal clearance after mounting 0-20 μm.

In the pulley unit structured as such, raceway curvatures are set to notless than 50.5% and not more than 52.0%, a radial internal clearanceafter mounting is set to less than 20 μm, or in a combination thereofcan make the axial internal clearance small. When the axial internalclearance becomes small, the axial deviation of the pulley 1 and therotor shaft 2 can be reduced to the minimum. Consequently, the rollers13 of the one-way clutch 3 and the rollers 33 of the needle rollerbearing 5 can be restricted in terms of a slip thereof in an axialdirection of the inner and outer raceway grooves, worsening interlockingthereof with raceway rings and a vibration due to a winding roll.Restricting the slip in the axial direction can restrict an exfoliationand an abrasion of the rollers 13, 33 and the raceway rings, and adecrease of life of a lubricant due to a heat generation.

Furthermore, setting the raceway curvatures to a small value such as notless than 50.5% and not more than 52.0% can restrict an inclinationcaused by a bending of the pulley unit in a case that a load of a belt Bworks on a free end portion of the pulley unit. As a result, it can berestricted that edge portions of the rollers 13 of the one-way clutch 3and the rollers 33 of the needle roller bearing 5 contact the racewaygrooves so as to be broken and generate heat. In addition, restrictingof the inclination of the pulley unit makes it hard for the belt 6 torun out so as to restrict a vibration and a noise.

In the embodiments, the radial internal clearance may be a negativeinternal clearance. The deep groove bearing 4 may be, instead, a ballbearing equipped with inner and outer rings separate from the pulley 1,the rotor shaft 2. The ball bearing may be arranged in another side ofthe one-way clutch 3, or a omitting the bearing arranged in another sideof the one-way clutch acceptable as well.

A raceway curvature of at least one of the inner and the outer rings ispreferably set to not less than 50.5% and not more than 51.5%. Morepreferably, the raceway curvatures of both the inner and the outer ringare set to not less than 50.5% and not more than 51.0%.

In this case, the relation between the radial internal clearance aftermounting and the axial internal clearance in case of one of the innerand the outer rings is shown in Table 5 and Table 6.

TABLE 5 radial internal clearance after axial internal mounting [μm]clearance [μm] 0  0 5  57˜65 10  81˜92 15  98˜112 20 113˜129 25 126˜14430 136˜157

TABLE 6 radial internal clearance after axial internal mounting [μm]clearance [μm] 0  0 5  48˜57 10  68˜81 15  83˜98 20  95˜113 25 105˜12630 115˜138

In Table 5, a raceway curvature of an inner ring is set to not less than50.5% and not more than 51.0%, the same of an outer ring is set to notless than 53.0% and not more than 53.5%. In Table 6, the equivalentsetting; not less than 52.0% and not more than 52.5% for the inner ring,not less than 50.5% and not more than 51.0% for the outer ring.

In reference to FIGS. 6 and 7, a pulley unit according to anotherpreferred embodiment of the present invention is described. A detailedexplanation on the part corresponding to FIGS. 1 and 3 is omitted. Incase of a pulley unit according to another preferred embodiment, anannular groove 42, to which a bottom end in a radial direction of theseal ring 21 is fitted, is formed on an outer radial face of the regionx3 in the rotor shaft 2. Since the other structure is similar to theabove-described, a detailed explanation on the structure and theoperation is omitted.

In case of the pulley unit, a radial internal clearance after mountingof the ball bearing 4 is set to such a relation as a value thereof issmaller than a radial internal clearance after mounting of the rollerbearing 5.

On premise that the above-mentioned relation of values regarding theradial internal clearance after mounting of the ball bearing 4 and theroller bearing 5 is satisfied, the radial internal clearance aftermounting of the ball bearing 4 is set to a range of −20-25 μm,preferably a range of −5-10 μm. The radial internal clearance aftermounting of the roller bearing 5 is set to a range of 5-35 μm,preferably a range of 5-20 μm.

FIG. 8 shows a relation between a radial internal clearance aftermounting and a life of the ball bearing 4. In FIG. 8, a horizontal axisdenotes a life (%), and the vertical axis denotes a radial internalclearance after mounting (μm). This relation is based on the radialinternal clearance 0 μm as the life 100%.

In case of the ball bearing 4, when the radial internal clearance is setto not more than −10 μm, a heat generation and a grease deteriorationoccurs, which leads to a drastic reduction of the life. Therefore, it isdesirable to set to not less than −5 μm.

As described, when the radial internal clearance after mounting of theball bearing 4 is set to a small value, a rattle in radial and axialdirections thereof reduces to the minimum. In that manner, the pulley 1and the rotor shaft 2 can be integrated at a high performance level anda rigidity against a moment load improves. Additionally, since the ballbearing 4 can reduce a freedom level of the rollers 13 of the one-wayclutch 3, whereby the action of the rollers 13 can be stabilized, and amicro slip and a skew of the rollers 13 can be reduced. Therefore, acontribution can be made to stabilization of the action of the one-wayclutch 3 and improvement of a durability of the one-way clutch 3 and thepulley unit.

The rotor shaft 2 is used as a respective inner ring of the one-wayclutch 3, the ball bearing 4 and the roller bearing 5, and the pulley 1is used as a respective outer ring of the one-way clutch 3, the ballbearing 4 and the roller bearing 5, wherein reduction of a number ofparts can be effective in cost reduction. Since the ball bearing 4, theone-way clutch 3 and the roller bearing 5 are incorporated in thatorder, a condition, in which the radial internal clearance of the rollerbearing 5 is larger, secures a favorable performance in theincorporating process.

When a wedge-like space is formed through arranging a cam face 21 on anouter peripheral face of the rotor shaft 2 providing an inner peripheralface of the pulley 1 is of a circular shape in section, a rotationalcentrifugal force advantageously makes it hard for the rollers 13 todeviate to a large interval side in the wedge-like space in a freestate. However, the cam face 10 may be arranged in the pulley 1 that is,on an outer ring element side.

Furthermore, like a pulley unit shown in FIG. 9, the present inventionincludes a structure in which the pulley 1 and the rotor shaft 2 are notused as both inner and outer rings respectively of the one-way clutch 3,the ball bearing 4 and the roller bearing 5. In this example, the innerrings 60, 61, 62 and the outer rings 63, 64, 65 are arrangedrespectively in the one-way clutch 3, the ball bearing 4 and the rollerbearing 5. The outer ring 63 of the one-way clutch 3 is extended atlength to both sides in the axial direction, and the outer rings 64 and65 of the ball bearing 4 and the roller bearing 5 are fixed byforce-fitting to the inner periphery of the extended portion. In such astructure, the relation between the respective radial internal clearanceof the ball bearing 4 and the roller bearing 5 is similar to thedescribed embodiment. In the structure, a radially-inward projectionpiece 12 d is arranged at two places in a circumference of the cage 12of the one-way clutch 3, and a notch 60 a is arranged at two positionsin a circumference of an end face of the inner ring 60. By engagingthem, the cage 12 and the rollers 13 are located in the axial direction.

In this embodiment, a rattle in the radial and the axial directions of aball bearing is reduced by setting the radial internal clearance aftermounting of the ball bearing to a small value. Therefore, a pulley and arotor shaft are integrated at a high performance level so as to improvea rigidity against a moment load. Additionally, the ball bearing canreduce a freedom level of a wedge member of the one-way clutch, therebyan acting performance of rolling bodies such as balls and rollers as thewedge member is stabilized, thereby a fine slip of the wedge memberreduces. As a consequence of these, an action of the one-way clutch isstabilized, and a durability thereof and the pulley unit is improved.

While there has been described what is at present considered to bepreferred embodiments of this invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of this invention.

What is claimed is:
 1. A pulley unit comprising: a pulley; a shaftrelatively rotatable with said pulley and concentrically arranged insideof said pulley; a one-way clutch interposed in an annular space betweensaid pulley and said shaft; and a ball bearing arranged adjacent to saidone-way clutch in an axial direction in said annular space, said ballbearing having an inner ring and an outer ring; wherein racewaycurvatures of said inner and outer rings of said ball bearing are set tonot less than 50.5% and not more than 52.0%, and said ball bearing isdisposed in one side of said one-way clutch, while a roller bearing isdisposed in the other side of said one-way clutch, and a radial internalclearance after mounting of said ball bearing is set to a smaller valuethan a radial internal clearance after mounting of said roller bearing.2. A pulley unit according to claim 1, wherein a radial internalclearance alter mounting of said bail bearing is set to less than 20 μm.3. A pulley unit comprising: a pulley; a shaft relatively rotatable withsaid pulley and concentrically arranged inside of said pulley; a one-wayclutch, interposed in an annular space between said pulley and saidshaft; and a ball bearing arranged adjacent to said one-way clutch in anaxial direction in said annular space; wherein a radial internalclearance after mounting of said ball bearing is set to less than 20 μm,and said ball bearing is disposed in one side of said one-way clutch insaid annular space, while a roller bearing is disposed in the other sideof said one-way clutch, and a radial internal clearance after mountingof said ball bearing is set to a smaller value than a radial internalclearance after mounting of said roller bearing.
 4. A pulley unitcomprising: a pulley; a shaft relatively rotatable with said pulley andconcentrically arranged inside of said pulley; a one-way clutchinterposed in an annular space between said pulley and said shaft; and aball bearing arranged adjacent to said one-way clutch in an axialdirection in said annular space, said ball bearing having an inner ringand an outer ring; wherein at least one of raceway curvatures of saidinner and outer rings of said ball bearing is set to not less than 50.5%and not more than 51.0%, and a radial internal clearance after mountingis set to less than 20 μm, and said ball bearing is disposed in one sideof said one-way clutch in said annular space, while a roller bearing isdisposed in the other side of said one-way clutch, and a radial internalclearance after mounting of said ball bearing is set to a smaller valuethan a radial internal clearance after mounting of said roller bearing.5. A pulley unit comprising: a pulley; a shaft relatively rotatable withsaid pulley and concentrically arranged inside of said pulley; a one-wayclutch interposed in an intermediate region (a first region) in an axialdirection in an annular space between said pulley and said shaft; a ballbearing disposed in one region (a second region) in said axial directionof said one-way clutch in said annular space; and a roller bearingdisposed in the other region (a third region) in said axial direction ofsaid one-way clutch in said annular space; wherein a radial internalclearance after mounting of said ball bearing is set to a smaller valuethan a radial internal clearance after mounting of said roller bearing.6. A pulley unit according to claim 5, wherein said radial internalclearance after mounting of said ball bearing is set to a range of −20to 25 μm.
 7. A pulley unit according to claim 6, wherein said radialinternal clearance after mounting of said roller bearing is set to arange of 5 to 35 μm.
 8. A pulley unit according to claim 5, wherein saidshaft is cantilevered, and said ball bearing is arranged in a basic endside of said shaft and said roller bearing is arranged in a free endside of said shaft.
 9. A pulley unit according to claim 5, wherein saidshaft is used as respective inner rings of said one-way clutch, saidball bearing and said roller bearing, and said pulley is used asrespective outer rings of said one-way clutch, said ball bearing andsaid roller bearing.
 10. A pulley unit according to claim 9, wherein aninner peripheral surface of said pulley as formed into an axiallysubstantial cylindrical shape and an outer ring raceway groove for saidball bearing is provided in said second region of said inner peripheralsurface of said pulley, and wherein an inner ring raceway groove forsaid ball bearing is provided in said second region of an outerperipheral surface of said shaft, flat cam faces are provided at severalpositions on a circumference of said first region of said outerperipheral surface of said shaft, and said third region of said outerperipheral surface of said shaft is formed into an axially substantialcylindrical shape.